Granular electrode and process of treating same



Patehted Aw- 4, I899- P. w.- Bos'sAnT. GBANULAR ELECTRODE AND PROCESS OF TREATING SAME.

(Application filed June 8, 1898.)

(No l.)

STATES 1 ATENT rricn.

PAUL-IV. BOSSART, OF MARIETTA, PENNSYLVANIA.

SPECIFICATION forming part of Letters Patent No. 622,413, dated April 4, 1899.

Application filed June 6, 1898. Serial No. 682,651. (No model.)

To aZZ whom it may concern:

Be it known that I, PAUL W. BOSSART, a citizen of the United States, residing at Marietta, in the county of Lancaster and State of Pennsylvania, have invented certain new and useful Improvements in Granular Electrodes and Processes of Treating the Same; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The object of this invention is to improve the microphonic power of telephones using granular electrodes, such as are common in transmitters, by securing the greatest possible microphonic distance as a quality of these granules combined with the maximum conductivity.

To this end my invention consists, partly, in

an improved process for treating the said granules and partlyin the granular electrodes themselves and in the instrument of which they form a distinctive feature, all as hereinafter more particularly set forth and claimed.

In the accompanying drawings, Figure 1 represents a vertical central section of a transmitter provided with my improved granular electrodes. Fig. 2 represents a detail perspective view, greatly enlarged, of one of the granules after treatment with the roughening solution. Fig. 3 represents a section through several of the same after coating and while in contact as used.

In said drawings, A designates the mouthpiece; B, the diaphragm; C, the back plate; D, the bed of granular electrodes, and E E the wire terminals.

I do not confine my invention to the particular form of telephonic instrument shown, but introduce it for purposes of illustration only. 4

Each granule making up the bed D consists of a carbon or other non-metallic body cl, having a roughened surface presenting on every side points and other projections 01 and be-- ing coated with a continuous metallic film d To produce these improved granular electrodes, I first take non metallic granules, preferably the carbon ones now commonly in use, and immerse them in a bath of sulfuric acid diluted with four or five times its volume'of water for several days. This treatment,by the action of the acid on the i1npurities which are always present in commercial carbon, produces the roughened condition of surface above described, having the points and projections d, which are plainly visible under the microscope. The surfaces of these granules are then moistened thoroughly with an aqueous solution of phosphorus and bisulfid of carbon in the proportion of twenty-five per cent. of the former to sevent y-five per cent. of the latter. They are next immersed in a nitrate-of-silver solution consisting of nine parts of water to one part of the nitrate. The function of the aforesaid bisulfid of carbon is to reduce the silver to a metallic state aided by the phosphorus. A coating of gold, silver, or copper is then applied and adheres to the metallic surface, forming a tough metallic film. This film is continuous andvery distinguishable from a crystalline or powdery layer of metal parti-. cles heretofore sometimes used. The best results are obtained whenthis film' or continuous layer is very thin. It should not materially lessen the prominences d of the roughened surfaces nor fill the hollows between them.

The microphonic power of a transmitter depends partly on the electric conductivity of its granular electrodes and partly on the microphonic distance of the same. Carbon and some other non-electric materials possess the highest known percentage of microphonic distance, but are more orless deficient in electric conductivity. Metallic electrodes are highly conductive, but are relatively deficient as to microphonic distance. By coatin g the carbon body of the granule with a continuous metallic film practically integral with the said body I produce a compound granule which secures the superior conductivity of the outer material, while retaining the microphonic distance of the other.

The irregularity of surface exemplified by points and other projections d is an impor tant improvement. Heretofore one of the main causes of trouble in transmitters has been the packing of the granular electrodes by reason of some change in position or vibration of the transmitter-case. Toobviate this evil, Various expedients have been resorted to-=-for example, coating the granules with oil or sticky substances. This has a tendency to interfere with the microphonic qualities of the carbon granules byimpeding that delicate sensitive vibration or change in distance between the granules on which depends the microphonic efficiency of this material as a variable resistance. My sulfuric-acid treatment is open to no such objection. It so roughens the surface of the granules that they will not pack too closely together, the points or projections cl holding them apart and leaving small air spaces and passages on every side of each granule. These points or proj ections d also prevent the said granules from slipping easily past each other and provide innumerable delicate pointed contacts of great conductivity, thus largely increasing the microphonic power of the granules. Fluctuations in vibration are what cause the microphonic action of the carbon granules, and the more sensitive they are to the slightest changes in vibratory motion the more efficient are they for such purposes.

In practice a microphonic transmitter provided with carbon granules thus roughened and coated is found far superior in power to one of similar construction containing carbon granules only or metallic granules only or smooth granules only of any material. I am able to make satisfactory use of a low grade of carbon thus treated and coated. Such granules mixed with ordinary carbon granules will greatly increase their serviceability.

1. A telephonic instrument having in circuit a body of non metallic metal-coated granular electrodes which have projections on all sides of their surfaces substantially as set forth. v

2. A carbon granule roughened and metalcoated and adapted to be used as a telephonic electrode substantially as set forth.

3. A layer or body of granular electrodes for telephonic use, each granule consisting of a carbon body and a continuous film of conducting metal, as distinguished from a crystalline or powdery layer of separate particles substantially as set forth.

4. A telephonic transmitter provided with a body of carbon electrodes, each electrode being a granule coated with a metallic continuous film and provided with projecting points substantially as set forth.

5. The process of producing or treating telephonic granular electrodes consisting in the following steps; first immersing carbon granules in dilute sulfuric acid until the surface is roughened and projections are formed thereon; secondly moistening this surface with a solution of phosphorus and bisulfid of carbon; thirdly immersing the granules, thus treated, in a nitrate-of-silver solution; and fourthly coating the surface thus prepared with a continuous film of metal adhering thereto substantially as set forth.

In testimony whereof I affix my signature in presence of two witnesses.

PAUL IV. BOSSART.

Witnesses JAMES W. KELLY, E. D. ROATH. 

